Refrigeration device

ABSTRACT

A refrigeration device includes: a refrigerator; a heat pipe that includes a condensation unit connected to the refrigerator in a manner that heat exchange is enabled and adapted to condense a refrigerant, includes an evaporation unit connected to a storage chamber housing an object that should be stored in a manner that heat exchange is enabled and adapted to evaporate the refrigerant, and includes a piping circulating the refrigerant between the condensation unit and the evaporation unit; a refrigerant chamber connected to the heat pipe and adapted to pool the refrigerant; and a heater that heats the refrigerant chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application No. PCT/JP2018/019112, filed on May 17, 2018, which claims the benefit of priority from Japanese Patent Application No. 2017-113191, filed on Jun. 8, 2017, the entire content of each of which is incorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates to refrigeration devices, and, more particularly, to a refrigeration device adapted to condense a refrigerant and then exhibit a cooling action by evaporating the refrigerant.

Description of the Related Art

Refrigeration devices configured to exchange heat between a refrigerator and a low-temperature storage chamber via a heat pipe connected to the cooling unit of the refrigerator are known (see, for example, patent literature 1). In the refrigeration device disclosed in patent literature 1, a gas entrapment for adjusting the pressure inside the heat pipe is provided.

[Patent literature 1] JP8-320165

The storage chamber of a low-temperature storage need be maintained in a low-temperature state stably. Therefore, various measures are taken to inhibit an increase in the temperature inside the storage chamber of the low-temperature storage. For example, the storage chamber is covered by a heat insulator having high heat insulation properties. Further, the door to take in or take out an object that should be stored in the storage chamber is configured as a double-entry door. The inner door is partitioned into a plurality of blocks to reduce the opening area through which the object that should be stored is taken in and out. The storage chamber is also configured to sound an alarm to alert the user when the door is open for a predetermined period of time or longer. The storage chamber is also configured to inhibit an increase in the temperature inside the storage chamber by means of an auxiliary source of cooling such as a liquefied gas as a measure to address temporary blackout.

We have studied refrigeration devices installed in a low-temperature storage and have recognized that there is room for improvement in related-art refrigeration devices for the purpose of maintaining the temperature of the low-temperature storage stably.

SUMMARY OF THE INVENTION

The present disclosure addresses the above-described issue, and an illustrative purpose thereof is to provide a technology for stabilizing the temperature of a low-temperature storage more properly.

An embodiment of the present disclosure relates to a refrigeration device. The refrigeration device includes: a refrigerator; a heat pipe that includes a condensation unit connected to the refrigerator in a manner that heat exchange is enabled and adapted to condense a refrigerant, includes an evaporation unit connected to a storage chamber housing an object that should be stored in a manner that heat exchange is enabled and adapted to evaporate the refrigerant, and includes a piping circulating the refrigerant between the condensation unit and the evaporation unit; a refrigerant chamber connected to the heat pipe and adapted to pool the refrigerant; and a heater that heats the refrigerant chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:

FIG. 1 is a perspective view showing a schematic structure of a low-temperature storage in which the refrigeration device according to the embodiment is installed;

FIG. 2 is a rear view showing a schematic structure of the low-temperature storage;

FIG. 3 is an enlarged view of area A bounded by the broken line in FIG. 2;

FIGS. 4A, 4B, and 4C are graphs showing the relationship between the temperature difference between the evaporation unit and the refrigerant chamber and the increase in the liquification temperature of the refrigerant;

FIGS. 5A, 5B and 5C graphs showing the relationship between the temperature difference between the evaporation unit and the refrigerant chamber and the increase in the liquification temperature of the refrigerant;

FIGS. 6A, 6B and 6C are graphs showing the relationship between the volume ratio and the ratio between the liquification temperature increase index A₁₀ occurring when the volume ratio is 10 and the liquification temperature increase index A_(n) occurring when the volume ratio is n; and

FIG. 7 is an enlarged view of an area including the condensation unit in the refrigeration device according to a variation.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify the invention.

Hereinafter, the embodiments will be described based on preferred embodiments with reference to the accompanying drawings. The preferred embodiments do not intend to limit the scope of the invention but exemplify the invention. Not all of the features and the combinations thereof described in the embodiments are necessarily essential to the invention. Identical or like constituting elements, members, processes shown in the drawings are represented by identical symbols and a duplicate description will be omitted. The scales and shapes shown in the figures are defined for convenience's sake to make the explanation easy and shall not be interpreted limitatively unless otherwise specified. Terms like “first”, “second”, etc. used in the specification and claims do not indicate a sequence or degree or importance by any means unless otherwise specified and are used to distinguish a certain feature from the others.

FIG. 1 is a perspective view showing a schematic structure of a low-temperature storage in which the refrigeration device according to the embodiment is installed. FIG. 2 is a rear view showing a schematic structure of the low-temperature storage. FIG. 3 is an enlarged view of area A bounded by the broken line in FIG. 2. FIG. 2 is a transparent view of the interior of the low-temperature storage. A low-temperature storage 1 is used to store a biological material such as a cell and a tissue of a living body, a medication, and a reagent. The low-temperature storage 1 includes a heat insulation box body 2 with an open top and a machine room 4 provided adjacent to the heat insulation box body 2.

The heat insulation box body 2 includes an outer box 2 a with an open top and an inner box 2 b with an open top. The space between the outer box 2 a and the inner box 2 b is filled with a heat insulator (not shown). The heat insulator is made from, for example, a polyurethane resin, a glass wool, and vacuum heat insulator. The space in the inner box 2 b defines a storage chamber 6. The storage chamber 6 is a space in which an object that should be stored is housed. The targeted temperature inside the storage chamber 6 (hereinafter, referred to as inside temperature as appropriate) is, for example, −50° C. or below.

A heat insulation door 8 is provided on the top surface of the heat insulation box body 2 via a packing. A heat insulation door 8 is fixed at one end to the heat insulation box body 2 and is provided to be rotatable around the one end. This heat insulation door 8 ensures that the opening of the storage chamber 6 can be opened or closed as desired. The other end of the heat insulation door 8 is provided with a handle 10 maneuvered to open or close the heat insulation door 8. An evaporation unit 26 of a heat pipe 16 described later is provided on the wall surface of the inner box 2 b toward the heat insulator. The interior of the storage chamber 6 is cooled due to evaporation of the refrigerant in the evaporation unit 26.

The machine room 4 is a space that houses a refrigeration device 12 according to the embodiment except that a part of a piping 28 of the heat pipe 16 and the evaporation unit 26 are provided in the heat insulation box body 2. The structure of the heat insulation box body 2 and the machine room 4 is publicly known so that a description of further details is omitted.

The refrigeration device 12 is a device capable of cooling the interior of the storage chamber 6 to an extremely low temperature of −50° C. or below. The refrigeration device 12 includes a refrigerator 14, the heat pipe 16, a refrigerant chamber 18, and a heater 20.

The refrigerator 14 is a device for cooling the condensation unit of the heat pipe 16. A publicly known refrigerator such as a Gifford-McMahon (GM) refrigerator, a pulse tube refrigerator, a Stirling refrigerator, a Solvay refrigerator, a Claude cycle refrigerator, and a Joule Thomson refrigerator can be used as the refrigerator 14. The refrigerator 14 includes a cooling unit 22 adapted to absorb the external heat. The structure of the refrigerator 14 is publicly known so that a description of further details is omitted.

The heat pipe 16 is a device for cooling a target of cooling by using the vaporization heat of the refrigerant and mediates heat exchange between the cooling unit 22 of the refrigerator 14 and the interior of the storage chamber 6. The heat pipe 16 includes a condensation unit 24, an evaporation unit 26, and a piping 28. The condensation unit 24 is connected to the cooling unit 22 of the refrigerator 14 in a manner that heat exchange is enabled. By causing the condensation unit 24 and the cooling unit 22 to exchange heat, the refrigerant in the condensation unit 24 is cooled, condensed, and turned into a liquid. For example, a refrigerant gas such as R740 (argon), R50 (methane), R14 (tetrafluoromethane), and R170 (ethane) can be used for the refrigerant.

More specifically, the condensation unit 24 includes, as shown in FIG. 3, a condensation fin 30 and a refrigerant passage 32 formed by the grooves of the condensation fin 30. The condensation fin 30 is connected to the cooling unit 22. The cold of the cooling unit 22 is conveyed to the refrigerant flowing in the refrigerant passage 32 via the condensation fin 30. The refrigerant in a gasified state is turned into a liquid in the refrigerant passage 32.

One end of the piping 28 is connected to the condensation unit 24. More specifically, one end of the piping 28 is connected to the refrigerant passage 32. Further, the other end of the piping 28 is connected to the evaporation unit 26. The refrigerant is circulated between the condensation unit 24 and the evaporation unit 26 via the piping 28.

The evaporation unit 26 is connected to the storage chamber 6 in a manner that heat exchange is enabled. In this embodiment, the evaporation unit 26 extends along the wall surface of the inner box 2 b toward the heat insulator. The refrigerant turned into a liquid in the condensation unit 24 flows into the evaporation unit 26 via the piping 28. In the evaporation unit 26, the refrigerant absorbs the heat from the storage chamber 6 and is evaporated. Evaporation of the refrigerant cools the interior of the storage chamber 6. The refrigerant turned into a gas in the evaporation unit 26 flows into the refrigerant passage 32 of the condensation unit 24 via the piping 28. The refrigerant is condensed again and turned into a liquid in the condensation unit 24.

The condensation unit 24 is provided vertically above the evaporation unit 26 Therefore, the refrigerant turned into a liquid in the condensation unit 24 is gravitationally transferred to the evaporation unit 26. In other words, the heat pipe 16 according to the embodiment is a so-called thermosiphon that circulates the refrigerant gravitationally.

As shown in FIG. 1, the piping 28 according to the embodiment includes a far-side connecting pipe 28 a and a near-side connecting pipe 28 b. One end of the far-side connecting pipe 28 a and one end of the near-side connecting pipe 28 b are connected to the refrigerant passage 32. Further, the evaporation unit 26 has a pipe shape, and the other end of the far-side connecting pipe 28 a is connected to one end of the evaporation unit 26. The other end of the evaporation unit 26 is connected to the other end of the near-side connecting pipe 28 b.

A portion of the refrigerant flows from the refrigerant passage 32 into the evaporation unit 26 via the far-side connecting pipe 28 a. The refrigerant mainly cools the far side of the inner box 2 b (rear side of the storage chamber 6) before it reaches the lower end of the evaporation unit 26. The refrigerant evaporated and turned into a gas in this process returns to the refrigerant passage 32 via the far-side connecting pipe 28 a. In other words, the liquefied refrigerant and the gasified refrigerant flow in the opposite directions in the evaporation unit 26 and the far-side connecting pipe 28 a. In this process, the liquid refrigerant flows near the circumference of the piping, and the gas refrigerant flows near the center of the piping.

Further, another portion of the refrigerant flows from the refrigerant passage 32 into the evaporation unit 26 via the near-side connecting pipe 28 b. The refrigerant mainly cools the near side of the inner box 2 b (front side of the storage chamber 6) before it reaches the lower end of the evaporation unit 26. The refrigerant evaporated and turned into a gas in this process returns to the refrigerant passage 32 via the near-side connecting pipe 28 b. In other words, the liquefied refrigerant and the gasified refrigerant flow in the opposite directions in the evaporation unit 26 and the near-side connecting pipe 28 b. In this process, the liquid refrigerant flows near the circumference of the piping, and the gas refrigerant flows near the center of the piping.

In other words, a refrigerant circulation path of the first system including the far-side connecting pipe 28 a and a refrigerant circulation path of the second system including the near-side connecting pipe 28 b are formed between the refrigerant passage 32 and the lower end of the evaporation unit 26. The heat pipe 16 may be structured to circulate the refrigerant by a capillary force. In this case the far-side connecting pipe 28 a is defined as an outward path unit, and the near-side connecting pipe 28 b is defined as a return path unit. A circulation path of refrigerant connecting the refrigerant passage 32, the outward path unit, the evaporation unit 26, and the return path unit is formed.

The refrigerant chamber 18 is a storage tank connected to the heat pipe 16 and pooling the refrigerant of the heat pipe 16. The refrigerant chamber 18 is connected to the refrigerant passage 32 of the condensation unit 24 via a pipe 34. The refrigerant can go back and forth between the heat pipe 16 and the refrigerant chamber 18 via the pipe 34. When the pressure in the heat pipe 16 is increased, a portion of the refrigerant moves from the heat pipe 16 to the refrigerant chamber 18. When the pressure in the heat pipe 16 is decreased, a portion of the refrigerant moves from the refrigerant chamber 18 to the heat pipe 16. In this way, the pressure in the heat pipe 16 is adjusted.

The heater 20 is a device for heating the refrigerant chamber 18. The heater 20 can be formed by a heater, a hot air blower, etc. that are publicly known. The availability of the heater 20 is switched based on the temperature of the evaporation unit 26 and the refrigerant chamber 18. In this embodiment, the availability of the heater 20 is controlled by a control unit 36. The control unit 36 is implemented in hardware such as a device or a circuit such as a CPU and a memory of a computer, and in software such as a computer program. Therefore, it will be obvious to those skilled in the art that the control unit 36 may be implemented in a variety of manners by a combination of hardware and software.

The control unit 36 receives a signal from a first temperature sensor 38. The first temperature sensor 38 is provided on the outer side surface of the pipe that forms the evaporation unit 26 and senses the temperature of the evaporation unit 26. The first temperature sensor 38 can substantially measure the temperature of the refrigerant in the evaporation unit 26. The control unit 36 also receives a signal from a second temperature sensor 40. The second temperature sensor 40 is provided on the outer side surface of the refrigerant chamber 18 and senses the temperature of the refrigerant chamber 18. The second temperature sensor 40 can substantially measure the temperature of the refrigerant in the refrigerant chamber 18.

The control unit 36 switches the availability of the heater 20 based on the signals received from the first temperature sensor 38 and the second temperature sensor 40 so that the temperature difference between the evaporation unit 26 and the refrigerant chamber 18 is equal to larger than a predefined value. For example, when the temperature difference between the evaporation unit 26 and the refrigerant chamber 18 is smaller than a predefined threshold value, the control unit 36 activates the heater 20 (turns it ON). When the temperature difference reaches a value derived by adding a predetermined margin to the threshold value, the control unit 36 stops the heater 20 (turns it OFF). In other words, the control unit 36 performs binary control between the availability of 0 and the availability of 100.

By heating the refrigerant chamber 18 by the heater 20 to induce a predetermined temperature difference between the refrigerant chamber 18 and the evaporation unit 26, the temperature at which the refrigerant is liquefied in the condensation unit 24 is increased. In other words, the internal pressure of the refrigerant chamber 18 is increased by heating the refrigerant chamber 18 by the heater 20. This increases the internal pressure of the heat pipe 16. As a result, the refrigerant is liquefied at a higher temperature in the condensation unit 24.

In the heat pipe 16 in which the refrigerant that is a gas at normal temperature is used, it is difficult to cool the storage chamber 6 efficiently until the refrigerant is liquefied in the condensation unit 24. This is because the efficiency of transporting the cold of a gas refrigerant is lower than that of a liquid refrigerant. For this reason, a long period of time is required until the inside temperature reaches a set temperature when the refrigeration device 12 is started, or until the inside temperature returns, after the heat insulation door 8 is opened, to the temperature before the door is opened.

By way of contrast, the refrigeration device 12 according to the embodiment includes the heater 20 for heating the refrigerant chamber 18. This increases the liquification temperature, i.e., the condensation temperature, of the refrigerant. Accordingly, the refrigerant is liquefied in a shorter period of time. As a result, the inside temperature of the storage chamber 6 is lowered more promptly. Accordingly, the temperature of the low-temperature storage 1 is stabilized more properly.

If the heater 20 is not provided, the temperature difference between the evaporation unit 26 and the refrigerant chamber 18 may not be of a desired value, depending on the environment in which the low-temperature storage 1 or the refrigerant chamber 18 are placed or the set inside temperature of the storage chamber 6. Absence of the heater 20 may limit the arrangement of the low-temperature storage 1 or the refrigerant chamber 18 or limit the set inside temperature in order to obtain a desired temperature difference. By way of contrast, provision of the heater 20 ensures obtaining a temperature difference between the evaporation unit 26 and the refrigerant chamber 18 more surely without impairing the flexibility of the arrangement of the low-temperature storage 1 or the refrigerant chamber 18 or the flexibility of the set inside temperature.

We have found that the liquification temperature of the refrigerant is increased as the temperature difference between the evaporation unit 26 and the refrigerant chamber 18 is increased. We have also found that, as the temperature difference is increased, the margin of increase in the liquification temperature relative to the margin of increase in the temperature difference becomes smaller. We have also found that the as the proportion of the volume (C2) of the refrigerant chamber 18 relative to the volume (C1) of the heat pipe 16 is increased, i.e., as the volume ratio (C2/C1) is increased, the liquification temperature of the refrigerant is increased. We have also found that, as the volume ratio is increased, the margin of increase in the liquification temperature relative to the margin of increase in the volume ratio is decreased. We have also found a preferable range of temperature difference and a preferable range of volume ratio.

FIGS. 4A-4C and FIGS. 5A-5C are graphs showing the relationship between the temperature difference between the evaporation unit and the refrigerant chamber and the increase in the liquification temperature of the refrigerant. FIG. 4A shows data for the refrigerant R740, FIG. 4B shows data for the refrigerant R50, and FIG. 4C shows data for the refrigerant R14. FIGS. 4A-4C show data obtained when the volume ratio is configured to be 1, 1.5, 2.5, 5, 7.5, and 10. FIG. 5A shows data for the volume ratio of 1.5, FIG. 5B shows data for the volume ratio of 2.5, and FIG. 5C shows data for the volume ratio of 5. FIGS. 5A-5C are single logarithmic charts in which the horizontal axis is a logarithmic axis.

In all refrigerants, the temperature difference and the increase in the liquification temperature have a positive correlationship. The volume ratio and the increase in the liquification temperature also have a positive correlationship. Accordingly, the margin of increase in the liquification temperature of the refrigerant is adjusted by adjusting the temperature difference and/or the volume ratio.

It is preferred that the heater 20 heats the refrigerant chamber 18 so that the temperature difference between the evaporation unit 26 and the refrigerant chamber 18 is 100° C. or more. This increases the liquification temperature of the refrigerant by 5° C. or more irrespective of the type of refrigerant or irrespective of the volume of the refrigerant chamber 18.

In an ordinary situation in which the low-temperature storage 1 is used, it is assumed that the inside temperature is increased about 5° C. by opening and then closing the heat insulation door 8. An increase of 5° C. of the inside temperature also produces an increase of about 5° C. of the refrigerant in the evaporation unit 26. This extends a period of time required for liquification by a duration required to lower the temperature by 5° C. when the refrigerant is liquefied in the condensation unit 24. This is addressed by increasing the liquification temperature of the refrigerant by 5° C. or more by configuring the temperature difference between the evaporation unit 26 and the refrigerant chamber 18 to be 100° C. or more. This inhibits the time required for liquification of the refrigerant from being extended due to the increase in the inside temperature. Accordingly, the inside temperature is lowered more rapidly.

The temperature difference between the evaporation unit 26 and the refrigerant chamber 18 is more preferably 150° C. or more and, still more preferably, 200° C. or more. This improves the flexibility in selection of the volume of the refrigerant chamber 18 and the flexibility in selection of the refrigerant. Further, the temperature difference is preferably 300° C. or less. By configuring the temperature difference to be 300° C. or less, the heat resistance required of the refrigerant chamber 18 is prevented from becoming excessive, and, ultimately, the manufacturing cost of the refrigeration device 12 or the low-temperature storage 1 is prevented from becoming excessive.

Further, it is preferred that the volume of the refrigerant chamber 18 is not less than 1.5 times the volume of the heat pipe 16, i.e., that the volume ratio is 1.5 or more. The liquification temperature of the refrigerant is hardly changed beyond the volume ratio of 10. Defining the increase I₁₀ in the liquification temperature occurring when the volume ratio is 10 as the reference (100%), the increase I_(1.5) in the liquification temperature occurring when the volume ratio is 1.5 is in excess of about 50% of the reference. Further, the increase I₅ in the liquification temperature occurring when the volume ratio is 5 is in excess of about 80% of the reference. The increase in the liquification temperature occurring when the volume ratio is 7.5 is about 90% of the reference. In other words, the margin of increase in the liquification temperature becomes smaller as the volume ratio is increased.

In view of flammability and significant greenhouse effect of the refrigerant, it is desired to reduce the amount refrigerant used. The amount of refrigerant used is proportional to the sum of the volume of the heat pipe 16 and the volume of the refrigerant chamber 18 (hereinafter, referred to as total volume as appropriate). In this background, the increase in the liquification temperature per a total volume occurring when the volume ratio is n (hereinafter, referred to as liquification temperature increase index A_(n)) will be studied. The liquification temperature increase index A_(n) is given by A_(n)=I_(n)/(1+n). I_(n) denotes the increase in the liquification temperature occurring when the volume ratio is n. The total volume includes the volume of the heat pipe 16. Hence, 1+n.

FIGS. 6A-6C are graphs showing the relationship between the volume ratio and the ratio between the liquification temperature increase index A_(n) occurring when the volume ratio is n and the liquification temperature increase index A₁₀ occurring when the volume ratio is 10. FIG. 6A shows data for the refrigerant R740, FIG. 6B shows data for the refrigerant R50, and FIG. 6C shows data for the refrigerant R14. FIGS. 6A-6C show data obtained when the temperature difference between the evaporation unit 26 and the refrigerant chamber 18 is configured to be 50° C., 100° C., 150° C., 200° C., and 250° C.

Defining the liquification temperature increase index A₁₀ occurring when the volume ratio is 10 as the reference, the liquification temperature increase index A_(n) (relative value) increase dramatically in the range of about n=0-1.5. In all combinations of the temperature difference and the refrigerant checked, the index has a maximum value near n=1-1.5. In a majority of combinations of the temperature difference and the refrigerant, the liquification temperature increase index A_(n) has a maximum value at n=1.5. In other words, the efficiency of liquification temperature increase per an amount of refrigerant used tends to be improved as the volume ratio n increases when n=0-1.5. Therefore, the advantage from increasing the liquification temperature of the refrigerant is achieved more surely by configuring the volume of the refrigerant chamber 18 to be not less than 1.5 times the volume of the heat pipe 16.

It is preferred that the volume of the refrigerant chamber 18 is not more than 5 times the volume of the heat pipe 16. Defining the liquification temperature increase index A₁₀ occurring when the volume ratio is 10 as the reference, the liquification temperature increase index A_(n) drops when n=1.5 or larger. The drop of the liquification temperature increase index A_(n) is generally linear. The slope of the drop changes significantly at one point, beyond which the index remains at a low level. Therefore, for compatibility between the liquification temperature increase efficiency per a volume of refrigerant used and the higher liquification temperature increase value, it is desired to configure the refrigerant chamber 18 to result in a volume ratio n smaller than the volume ratio n occurring at the point of change in the slope. As shown in FIGS. 6A-6C, the point of change in the slope of the drop is near the volume ratio 7.5 and is found between the volume ratio of 7.5 and the volume ratio of 5.

Therefore, by configuring the volume of the refrigerant chamber 18 to be not more than 5 times the volume of the heat pipe 16, the advantage from increasing the liquification temperature of the refrigerant is achieved, while, at the same time, the size of the low-temperature storage 1 is inhibited from increasing due to the increase in the volume of the refrigerant chamber 18, and an increase in the amount of refrigerant used is inhibited. In other words, by configuring the volume ratio to be not less than 1.5 and not more than 5, the liquification temperature of the refrigerant is increased efficiently while, at the same time, the dimension of the refrigerant chamber 18 is inhibited from being excessive and the amount of refrigerant used is inhibited from increasing.

The advantage from configuring the volume ratio to be not less than 1.5 and not more than 5 is described above with reference to FIG. 4A, based on the increase in the liquification temperature occurring when the refrigerant is R740 and the temperature difference is 250° C. The same description also applied in the case of other refrigerants and other temperature differences.

The liquification temperature of the refrigerant can be increased further depending on the combination of the temperature difference and the volume ratio. For example, the liquification temperature of the refrigerant can be increased by 10° C. or more in the case the volume ratio is 1.5 or larger and the temperature difference is 200° C. or more. Further, the liquification temperature of the refrigerant can be increased by 15° C. or more in the case the volume ratio is 2.5 or larger and the temperature difference is 250° C. or more. We have confirmed that the liquification temperature of the refrigerant can be increased also by 15° C. or more by configuring the volume ratio to be 4 or larger and configuring the temperature difference to be 180° C. or more.

As shown in FIG. 3, the pipe 34 in the refrigeration device 12 according to the embodiment that connects the refrigerant chamber 18 and the heat pipe 16 is connected to the condensation unit 24 at a position vertically above the piping 28.

It is possible that air enters the piping 28 or the evaporation unit 26 of the heat pipe 16 from outside. When the liquification temperature of oxygen or nitrogen included in the air is lower than the liquification temperature of the refrigerant, oxygen or nitrogen entering the heat pipe 16 is collected as a gas in the condensation unit 24 at least temporarily. Since oxygen and nitrogen are in a gaseous state, the gas begins to be collected in a space vertically above the condensation unit 24. Collection of oxygen or nitrogen in the condensation unit 24 hinders liquification of the refrigerant in the condensation unit 24. Further, the major portion of the condensation unit 24 will be occupied by oxygen or nitrogen. If oxygen or nitrogen is liquefied and mixed in the refrigerant as a result, the liquification temperature of the refrigerant could be changed. In this case, it may become difficult to maintain the inside temperature as set.

By way of contrast, connecting the pipe 34 and the condensation unit 24 at a position vertically above the position of connection between the piping 28 and the condensation unit 24 allows the air collected in the condensation unit 24 to be recovered in the refrigerant chamber 18 smoothly. In other words, the refrigerant chamber 18 has a function of recovering the gas mixed in from outside. This mitigates the hindrance of liquification of the refrigerant and inhibits the change in the liquification temperature of the refrigerant.

It is more preferred to connect the pipe 34 and the condensation unit 24 at the upper vertical end of the condensation unit 24 as shown in FIG. 7. This makes it possible to recover the gas entering the heat pipe 16 from outside in the refrigerant chamber 18 rapidly. FIG. 7 is an enlarged view of an area in the refrigeration device according to a variation including the condensation unit.

As described above, the refrigeration device 12 according to the embodiment includes the refrigerator 14, the heat pipe 16, the refrigerant chamber 18, and the heater 20. By heating the refrigerant chamber 18 by the heater 20, a desired temperature difference can be produced between the refrigerant chamber 18 and the evaporation unit 26. This increases the liquification temperature of the refrigerant and lowers the inside temperature more rapidly. Consequently, the inside temperature is lowered to the set value rapidly even when the inside temperature is increased because of the opening of the heat insulation door 8. Accordingly, the temperature of the low-temperature storage 1 is stabilized more properly.

Further, in one embodiment, the heater 20 heats the refrigerant chamber 18 so that the temperature difference between the evaporation unit 26 and the refrigerant chamber 18 is 100° C. or more. In this case, the temperature of the low-temperature storage 1 is stabilized more properly. Further, in one embodiment, the volume of the refrigerant chamber 18 is not less than 1.5 times the volume of the heat pipe 16. In this case, the temperature of the low-temperature storage 1 is stabilized more properly.

The invention is not limited to the embodiment described above and various modifications such as design changes may be made based on the knowledge of a skilled person, and the modified embodiments are also within the scope of the present invention. New embodiments created by modifying the embodiment described above will provide the combined advantages of the embodiment and the variation.

Optional combinations of the aforementioned constituting elements, and implementations of the invention in the form of methods, apparatuses, and systems may also be practiced as additional modes of the present invention. 

What is claimed is:
 1. A refrigeration device comprising: a refrigerator; a heat pipe that includes a condensation unit connected to the refrigerator in a manner that heat exchange is enabled and adapted to condense a refrigerant, includes an evaporation unit connected to a storage chamber housing an object that should be stored in a manner that heat exchange is enabled and adapted to evaporate the refrigerant, and includes a piping circulating the refrigerant between the condensation unit and the evaporation unit; a refrigerant chamber connected to the heat pipe and adapted to pool the refrigerant; and a heater that heats the refrigerant chamber to a temperature higher than that of the evaporation unit.
 2. The refrigeration device according to claim 1, wherein the heater heats the refrigerant chamber so that a temperature difference between the evaporation unit and the refrigerant chamber is 100° C. or more.
 3. The refrigeration device according to claim 1, wherein a volume of the refrigerant chamber is not less than 1.5 times a volume of the heat pipe. 